1. Field Of The Invention
This invention relates generally to apparatus for dewatering slurries in mining and metallurgical operations.
In particular, this invention pertains to a sector body for use in a rotary disc vacuum filter.
2. State of the Prior Art
Rotary disc vacuum filters are well-known in the mining and metallurgical arts for dewatering slurries. A rotary disc vacuum filter typically comprises a plurality of filter discs mounted parallel to each other along and perpendicular to the axis of an elongate center barrel for rotation about the axis. A filter disc typically comprises a plurality of wedge-shaped sector assemblies, each assembly comprising a sector body and a bell member. The sector body is covered by a filter medium made of a flexible material such as a woven cloth or a wire screen.
During a first portion of a rotation of the center barrel, each sector assembly is immersed in the slurry to be filtered. When the sector assembly is immersed in the slurry, suction is applied to draw liquid from the slurry through the filter medium and thence via the sector body to the bell member. From the bell member, this filtrate liquid passes into the center barrel for removal to a storage or discharge means. Particulate matter in the slurry cannot pass through the filter medium, and hence forms a cake on the exterior surface of the filter medium. During a subsequent portion of the same rotation of the center barrel, the sector assembly is lifted out of the slurry. When the sector assembly is out of the slurry, positive air pressure is applied either continuously or in bursts via the sector body to shake the filter medium in order to dislodge the cake of particulate matter that has formed thereon.
In one type of sector assembly known to the prior art, the sector body comprises a perforated hollow structure. When the sector assembly is immersed in the slurry, a vacuum is provided in the interior of the hollow sector body whereby liquid can be sucked through the filter medium into the interior of the sector body for passage therethrough to the interior of the bell member and thence to the center barrel. When the sector body is rotated out of the slurry, pressurized air is blown either as a continuous or in bursts through the perforations in the sector body to shake or snap the covering filter medium.
In another type of sector assembly known to the prior art, the sector body is a solid body provided with a pattern of drainage channels on its surfaces. The lands between these channels support the filter medium away from the interior of the channels. When the sector assembly of this type is immersed in the slurry, a vacuum is provided in these drainage channels to draw liquid through the filter medium and thence along the drainage channels into the bell member for passage to the center barrel. When the sector assembly is rotated out of the slurry, a source of positive air pressure is applied along the channels to blow against the filter medium, thereby shaking or snapping the filter medium in order to remove filter cake therefrom.
The sector body of the second type of sector assembly described above, i.e., a sector body having surface drainage channels, may be perforated hollow structure instead of a solid body. Where surface drainage channels are provided on a perforated hollow sector body structure, suction and positive air pressure can be applied via the interior of the sector body through the perforations on the sector body. A major portion of the flow of filtrate liquid through the filter medium passes to the bell member along the surface drainage channels, although a certain amount of filtrate liquid also enters the interior of the sector body through the perforations.
In any of the types of sector assemblies described above, the sector body covered with the filter medium is coupled to the bell member in such a way as to enable filtrate liquid to flow either along drainage channels on the surface of the sector body or through the interior of the sector body into the bell member. The filtrate liquid passes through the bell member into the center barrel. The filtrate liquid passed into the center barrel from all the discs of the dewatering apparatus is typically removed from the center barrel by vacuum and passed to an appropriate means for further treatment and/or discharge or reuse.
A detailed description of a particular type of rotary disc dewatering apparatus now known to the prior art is provided in co-pending U.S. patent application Ser. No. 804,829, which is assigned to Envirotech Corporation.
Materials such as woven cloth and metal screens have been used in the prior art as filter media. Such fabrics periodically wear out and have to be replaced. Repeated flexing of a filter medium, particularly flexing due to the shaking and/or snapping of the filter medium to dislodge the filter cake therefrom, is a major cause of wear.